Process of making shaped bodies capable of being sintered



June 19, 1945. w -1 2,378,539

\ PROCESS OF MAKING SHAPED BODIES CAPABLE OF BEING SINTERED Filed se xl4, 1941' Inventor: .Walther Dawihl '10s JWZW His Attorney;

Patented June 19, 1945 PROCESS OF MAKING SHAPED BODIES CAPABLE OF BEINGSINTERED Walther Dawihl, Kohlhasenbruek. near Berlin,

Germany; vested in the dian Alien Property Custo- -Applieation September4, 1941, Serial No. 409,501

. In Germany June 4, 1940 3 Claims.

Shaped bodies particularly of the kind made of hard metal alloys haveheretofore usually been produced in such a way that a powder, forinstance a mixture of powdered tungsten carbide a p wdered cobalt, wasplaced into molds either in the dry state or with an addition of amoistening liquid, such as water or acetone, and subsequently pressed,after which a greater number its plasticity the extruded bar can readilybe seetioned by customary means, such as knives or cutting wires. It ispossible by means of the novel method to produce per hour many hundreds.of

units of shaped bodies of uniform size, measuring for instance by 10 bymm. along the edges,

such as are frequently used as blanks for cuttingof thesmallpressed-powder bodies thus obtained were sintered conjointly in afurnace and then,

after being machined, again placed in a furnace intervals in order thata portion of the mass, While retained in thepres's during itsstand-still, can first be de-aerated and then suddenly set'under an airor gas pressure, if necessary, of several atmospheres. Each section ofthe forward movement of the flowing mass corresponds in length to thesection of the mass that is being acted upon by vacuum, airor gas.Therefore, the bar extruded from the mouth-piece of the press has beenuniformly subjected over its entire length to the action of the vacuum,air or gas. Further more. the extruded bar is divided in manner knownper se into sections of the required length. Such sections aresubsequently sintered, machined to the desired shape, andfinish-sintered. As a binder, use can be made of Wate Or c iq d such asfor instance lycerine or mixtures containing glycerlne, or alsosolutions, for instance, of resins in, the liquids just referred to. Inconsequence of de-aeration, the air trapped in the tips insert-piecesand pins.

In order that the invention may be readily understood, one example ofconstruction of an ex- .trusion press suitable for carrying out theprocess is represented diagrammatically on the accompanyingdrawing-showing a vertical section.

The extrusion press consists of a cylindrical casing 5 having a taperedfront portion, and which encloses a longitudinall arranged shaft 2 aswell as a worm gear 56 secured thereto. At the rear end of the casing i,a feed hopper 4 is provided for the powder which is mixed with a binder,for instance water or glycerine. Said hopper may contain, as shown, apiston 5, the action of which presses the powder t into the casing I,avoiding the inclusion of an unduly great amount of air. The centralportion of the casing i is separated from the rear and front parts ofthe casing by means of two screen plates 8 inserted therein and securedto bushings l of the shaft 2. To the wall of said central portion isfitted a tube 9 communicating, on the one side, with a pressure chamherby means of a shut ofl valve iii and, on the other side, with a vacuumsource by means of a shut-ofl valve H so that eitherthe air contained inthe space between the two screen plates 8 can be exhausted or the spaceitself set under pressure. In this case, layers of the moist pastypowder-mixture, adhering to the screen plates 8,

- form a sufliciently tight air seal in the central pores of the hardmetal mass is first exhausted and then, owing to the sudden stream ofgas entering under sumcient pressure, the total mass is.

compressed, and the cavities which wer filled with the vapour from themoistening liquid dur-- ing the de-aeration, are compressed to a largeextent and closed, thus liquefying such evaporated parts. The gas usedcan either be air or, in the case of powders sensitive to oxygen,hydrogen or other gases. In general, the pressure of the gas introducedwill be adjusted to one atmosphere; however, in certain cases, pressuresof several atmospheres may also be adopted. Owing to portion of thecasing, so that the action of the vacuum or of the pressure, as the casemay be,

can only become eflective in the said central portion of the casing. Inthe mouth-piece [2 of the extrusionpress is inserted a spring sleeve IS,the rear part M of which is attached to the inner wall of themouth-piece l2, for instance by soldering, welding, or riveting. Thefront end of the sleeve I3 is subjected to the pressure exerted by alubrieating liquid, such as water or oil, introduced into themouth-piece by means of two tubes l5. At

the front end of the sleeve l3, the lubricatin liquid is projected ontothe bar, preventing the latter from adhering to the inner wall of themouth-piece, which is an important featurein view of the risk involvedfor the bar to stick to the mouth-piece during each interruption of theforward movement of the bar. However, the lubricating liquid which iscontinuously ied onto the surface oi'the' bar, through the medium of thespring sleeve i3, causes the bar to be extruded very reliably in aconstantly uniform' condition from the mouth-piece l2. Directly in frontof said mouth-piece, cutting tools of any desired description'may bearranged to cut the bar into small shaped bodies. If desired, the piston5 may be inserted with a perfectly tight flt to permit of the presschamber being set under vacuum or pressure as far as the said piston..With this arrangement, the first of the two screen plates may bedispensed with.

What I claim as new and desire to secure by Letters Patent 0! the UnitedStates is:

1. The process or making shaped forms oi. sinterable powder mixtures ofhard metal alloys and the like which comprises intermittently advancingthe powdered mixtures longitudinally through a press having threesuccessive zones divided by transverse screens, interrupting the advanceof the material at short intervals and during said interruptionsubjecting the material in the intermediate zone between the screens tode-aeration by vacuum, subjecting the material to superatmospheric gaspressure and finally extruding the treated material.

2. The process oi making shaped forms of sinterable powder mixtures 01'hard metal alloys and the like and a liquid binder, which comprisesintermittently advancing the powdered mixtures longitudinally through apress having three successive zones divided by transverse screens,interrupting the advance of the material at short intervals and duringsaid interruption subjecting the material in the intermediate zonebetween the screens to de-aeration by vacuum, subjecting the material tosuperatmospheric gas pressure and finally extruding the treatedmaterial.

3. The process of making shaped forms of sinterable powder mixtures ofhard metal alloys and the like and a liquid binder, which comprisesintermittently advancing the moistened powder mixture longitudinallythrough a press having three successive zones divided by transversescreens, interrupting the advance of the material so that eachsuccessive portion will pause 1n the intermediate zone between thescreens, subjecting such portion to de-aeration by vacuum andsubsequently to superatmospheric gas pressure, advancing the materialand finally extruding said treated material.

WALTHER DAWIHL.

